1. Field of the Invention
The present invention relates to a spinning solution for chitosan fiber and a method for fabricating the same, and more particularly to a spinning solution for industrial production of pure chitosan fiber and a method for fabricating the same.
2. Background of the Invention
The pure chitosan fiber is made from a raw material of high purity chitosan by wet spinning, is positively charged, has an excellent broad-spectrum antibacterial property, is biodegradable, has a function of promoting wound healing and hemostasis, and has advantages like excellent good hygroscopicity and air permeability. Therefore, it has great potential in applications such as medical products, dressing, antibacterial textile, and the like, and can create a significant social benefit.
Due to the process related reasons, the current spinning solution for producing chitosan fiber leads to a finished product with relatively low fiber dry breaking strength, relatively small dry breaking elongation, poor spinnability, and low functionality.
In the current patents about the production of chitosan fiber, there are various processes for fabricating chitosan spinning solution. In both production in a laboratory and industrial production in limited quantities, chitosan powder is formed into a chitosan fiber spinning solution. Up to now, flake chitosan has not been used to form chitosan fiber spinning solution. Nowadays, the high-performance pure chitosan fiber needed in the market requires that the flake chitosan with a high and ultra-high deacetylation degree and an ultra-high viscosity should be used as the raw material. The detailed description follows.
(I) 1. A higher deacetylation degree of chitosan facilitates the attachment and growth of cells on the chitosan film (fiber), a better compatibility with cells, and a less damage to cells. In contrast, the chitosan film (fiber) with a low deacetylation degree (<70%) has poor compatibility with cells, does not facilitate the attachment and growth of cells, and has a certain damage to cells. In this regard, reference can be made to “Effects of different deacetylation degrees on the compatibility between a chitosan film and corneal stroma cells”, 2006; 23 (4): 800˜804, JOURNAL OF BIOMEDICAL ENGINEERING.
2. As the deacetylation degree of chitosan increases, the chitosan has an improved antibacterial activity. In this regard, reference can be made to “Antibacterial activity of chitosan with different deacetylation degrees”, Vol. 10, No. 4, JOURNAL OF SHANGHAI FISHERIES UNIVERSITY.
From the above two aspects, it can be found that a higher deacetylation degree of chitosan leads to the spun chitosan fiber has an improved functionality.
(II). The relationship between the viscosity and the molecular weight is indicated by the Mark-Houwink law:[η]=kMα,where η is the viscosity in mpa·s; K is a constant which is not so associated with the system properties, and has a temperature-dependent value; M is the relative molecular mass; and α is a value associated with the molecular weight. As can be seen, the decrease in the chitosan viscosity in fact results from the decrease of the molecular weight. It is well known that, for the chitosan with a larger molecular weight, the spun chitosan fiber has a higher dry breaking strength. From the view point of spinning a high-performance pure chitosan fiber, it is superior to use a flake chitosan raw material with the original chitosan molecular chain structure.
The current process for fabricating a spinning solution suffers from the following drawbacks.
Firstly, the current raw material for producing chitosan fiber has a medium deacetylation degree (75%<D·D<89%). As a result, the produced fiber has a low bacteriostasis rate, and has a poor compatibility with cells.
Secondly, the process, in which the flake chitosan is broken into powder and then the chitosan powder is formed into a chitosan fiber spinning solution, increases the procedure and cost. More importantly, this process destroys the molecular chain structure of chitosan. If the flake chitosan with a viscosity of 1000 mpa·s is ground into a powder of 1-2 mm, the viscosity may decrease to 700 mpa·s by about 30%. The resulting spinning solution has a reduced fiber forming property. In addition, the finished fiber has a relatively low dry breaking strength, a low dry breaking elongation, and a poor spinnability.
Thirdly, during fabricating a chitosan fiber spinning solution from flake chitosan, the dissolving rate in the prior art is too slow, and the product quality sometimes fluctuates. In theory, when the flake chitosan is decalcified and deproteinizated, a lot of space develops between tissues in the flake chitosan and may be filled with air. In addition, the flake chitosan raw material is formed by stacking 2 or more sheets, and there is also a lot of space among them. When the acetic acid solution contacts the flake chitosan, a viscous dissolved solution is formed on the surface of the flake chitosan raw material and wraps the surface of the flake raw material. As a result, the gas in the space of chitosan can not escape and the solution can not enter the space, which leads to a long time for dissolving the flake chitosan raw material. During industrial production, if a batch of flake chitosan raw material is put into a dissolving kettle, a phenomenon may be found in which some of the flake chitosan raw material has been dissolved, while the other has not been dissolved. Once all of the flake chitosan raw material has been dissolved, the chitosan solution which was dissolved early has partly hydrolyzed, and exhibits a decreased viscosity. Such a spinning solution tends to lead to broken ends during spinning, and is no longer able to spin a high performance fiber. Therefore, this approach cannot meet the requirements in the industrial continuous production, and always restricts the development of pure chitosan fiber in our country.
Therefore, there is an urgent need for solving the problem of fabricating high-performance pure chitosan spinning solution with a flake chitosan raw material in the industrial production.